Intermetallic Kinetic Growth and Latent Solder Joint Shear Failure Modeling
Latent solder joint failure stems from thermally activated intermetallic growth and Kirkendall voiding, requiring high-speed shear testing to detect interface embrittlement.
Brittle Fracture Cleavage
Failure Mechanism
Rapid crack propagation along low-index crystallographic planes occurs in metal alloys subjected to high-strain-rate loading. This brittle fracture cleavage represents a catastrophic failure mode in microelectronics because it occurs with negligible plastic deformation. It produces flat, reflective surfaces.
Interconnection Failure
Ball grid array joint failure under shock or vibration testing frequently manifests as this type of separation at the intermetallic compound boundary. In these assemblies, brittle fracture cleavage usually occurs within the nickel-tin or copper-tin intermetallic layer when the printed circuit board is subjected to drop testing. It is driven by the stiffness of the intermetallic compound, which cannot accommodate the localized elastic energy released during high-impact loading.
Inspection Detection
Surface analysis of failed joints using scanning electron microscopy reveals distinct river patterns that point back to the origin of the crack. Since this failure occurs without extensive plastic deformation, it cannot be detected by optical inspection of the board surface prior to complete electrical open circuit development. Consequently, board designers must employ underfills or corner bonding to mitigate high tensile stresses at the outermost solder joint rows, particularly when using lead-free alloys which are inherently stiffer and more prone to brittle failures than lead-bearing solders.